Take it from me, most of that is BS. The ONLY thing that makes it possible is rooting the phone, flashing a modified kernel and keeping literally all of the things that make the phone a smartphone off. All of those people that talk about getting two days battery life out of the Evo I can guarantee you they barely even use the phone. I have to keep Tango off, yahoo off, qik off, 4G off, etc. If I were to actually USE half the features of the phone during the day it'd be dead in a matter of a few hours.
The SBC kernels have been a god send, but there have been several people that reported that using them mucked up their phones so its risky. The main thing they say do is disable mobile data.. which basically means none of your apps or email update in the background until you turn the screen on. For a smart phone thats pretty wack.